From what does the mesoderm form?

Answer 1

Diagram and all!
http://en.wikipedia.org/wiki/Mesoderm

Answer 2

"The morphogenic process called gastrulation ios a dramatic rearrangement of the cells of the blastula to form a three-layered embryo with a primitive gut. Although gastrulation differs in detail from one animal group to another, the process is driven by the same general mechanisms in all species: changes n cell motility, changes in cell shape, and changes in cellular adhesion to other cells and to molecules of the extracellular matrix. The result of gastrulation is that some of the cells at or near the surface of the blastula move to an interior location, and three cell layers are established. The three-layered embryo is called the gastrula. The positioning of the cell layers in the gastrula allows cells to interact with each other in new ways."
"The three layers produced by gastrulation are embryonic tissues collectively termed the embryonic germ layers. The ectoderm forms the outer layer of the gastrula; the endoderm lines the embryonic digestive tract; and the mesoderm partly fills the space between the ectoderm and the endoderm. Eventually, these three cell layers develop into all the tissues and organs of the adult animal."
Specifically, from the mesoderm the following tissues are derived: notochord; skeletal system; muscular system; muscular layer of stomach, intestine, etc., excretory system, circulatory and lymphatic system, reproductive system (except germ cells), dermis of skin, lining of body cavity, adrenal cortex.